1. Field of the Invention
This invention relates to a method and apparatus for effecting bi-directional communication within a given frequency band over an existing CATV coaxial cable system linking two or more remote points or stations.
2. Description of the Prior Art
With the advent in recent years of Community Antenna Television Systems, extensive and costly cable networks have been installed in many communities to link a central TV signal source, such as a mountain top antenna, to a plurality of remote subscribers. Once these cable networks are installed it is naturally tempting and desirable to utilize their signal carrying capacity to effect other forms of communication between the linked points or stations.
The presently used methods of providing such ancillary, bi-directional communications employ a radio frequency band of 5 - 32.5 MHz for upstream transmissions and the normal television carrier band of 50 - 300MHz for downstream transmissions. To enable such upstream carriage from a subscriber's home, for example, to a remotely located control center, additional equipment must be installed in the existing CATV system. Each downstream amplifier in the system must be provided with a diplexing filter to separate the 5 - 32.5MHz band from the 50 - 300MHz band, an upstream amplifier to compensate for the attenuation to the signal in the 5 - 32.5MHz band, and a combiner to rejoin the two bands back onto the same cable. In a similar manner, filters must be provided at each bridging amplifier to route the 5 - 32.5MHz band from the off-trunk splitter, around the bridging amplifier, and into the upstream amplifier. These necessary modifications are both costly and troublesome, and thus represent a considerable drawback when using an existing CATV system for ancillary, bidirectional communications.